Tenebrescent display tube



Oct. 4, 1966 R. SPENCER 3,277,241

TENEBRESCENT DI S PLAY TUBE Filed June 5, 1963 2 Sheets-Sheet l INVENTOR. GORDON SPENCER Oct. 4, 1966 G. R. SPENCER 3,277,241

TENEBRESCENT DISPLAY TUBE 2 Sheets-Sheet 2 Filed June 3, 1963 FIG.4 F|G.5

INVENTOR. F IG. 6 GORDON R. .SPENCER AGE/VT nited States Patent 3,277,241 TENEBRESCENT DISPLAY TUBE Gordon R. Spencer, Norwood, Mass, assignor to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed June 3, 1963, Ser. No. 284,931 4 Claims. (Cl. 1787.5)

This invention relates to display tubes generally, and has particular reference to a traveling image display tube having a target of tenebrescent material for generating a visible image in response to impingement by an electron beam.

A tenebrescent display tube of the presently described type utilizes the phen-omonon of tenebrescence, which is the particular characteristic of certain materials to change their light-absorbing properties upon bombardment by high energy electrons. In accordance with this invention, a continuously moving target of tenebrescent material passes through the path of a scanning electron beam, which is modulated with an incoming signal generated as by radar or other one-dimensional sensors. Upon suc-h bombardment of the target, the areas subjected to electron bombardment become. visible, thus producing a visible image corresponding to the modulated input signal. Suitable means is also provided for subsequently erasing the visible image in accordance with this invention.

In recognition of the demand for a moving visible display for use in aircraft and other vehicle, the prior art has taught various methods of attempting to achieve the objective of obtaining a continuously moving maplike display whose motion is synchronized with the motion of the vehicle, which display will not appreciably decay in contrast as the line-scan information moves from the beginning to the end of the display. Scan converters have been considered for this purpose but require a relatively large amount of associated equipment. Another system utilizes a traveling image orthicon type of tube having a moving target, which, however, still necessarily involves a separate display unit since the orthicon tube provides electrical rather than visible output. A moving target direct-view storage tube, also suggested, has a serious disadvantage in that the target structure in such a tube is relatively delicate, easily damaged and easily contaminated; the resolution, furthermore, is limited by the electron optics of the flood electron source.

Accordingly, it is a primary object of this invention to provide a display tube which is efficient under normal ambient illumination.

Another important object is to provide a display device embodying a moving target for visual presentation of a display format and which moves at a uniform and relatively slow rate.

A further object is the provision of an efficient display'device which has substantially uniform contrast throughout the display and which is observable in a realtime situation.

Another object is to provide a display device of the character described which is relatively simple and easy to construct and operate, efficient in its operation, and which does not require complicated or intricate accessory equipment to produce the resultant display in a form suitable for viewing.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a front vertical axial sectional view through a display tube embodying the invention;

FIG. 2 is a side vertical axial sectional view of the display tube shown in FIG. 1;

FIG. 3 is an enlarged front elevational view of the target or scroll structure; and

FIGS. 4, 5 and 6 are enlarged fragmentary sectional views of a modified scroll illustrating three stages in the manufacture thereof.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, the tube shown in FIGS. 1 and 2 comprises an envelope 10 of glass or similar transparent material. Envelope 10 comprises a main body portion 11 having a relatively slender neck portion 12 extending from the upper end thereof. Neck portion 12 of the envelope contains an electron gun 13 which may be of any conventional type and which may be connected by suitable externally extending leads 14 to suitable sources of electrical potentials whereby the gun may be operated to produce a beam of electrons which is directed into the main body portion 11 of the envelope.

Within body portion 11 there is provided a moving target 15 which is adapted to be scanned by the electron beam from gun 13. The target comprises a scroll or ribbon 16 in the form of an endless belt which is mounted over a framework 17 (FIG. 3) which includes a pair of rollers or drums 18 and 19 at opposite ends of the belt, the lower drum 19 being suitably connected to external means for rotating the target. The framework 17 may be of any suitable structure and in the embodiment shown in FIG. 3 comprises a pair of parallel spaced uprights 20 and 21 having the drums, shafts or rollers 18-19 located between their opposite ends. The drums are suitably rotatably mounted in the uprights 20-21 and the entire framework is mounted as by resilient spring members 22 carried by the uprights, which spring members which engage and interfit with recesses formed in the inner walls of the envelope portion 11. The belt or scroll 16 is mounted over the drums 18-19 and is consequently movable upon induced rotation of one or both of the drums. Extending laterally from lower drum 19 (FIG. 3) is a drive shaft 23 which extends outwardly through the side wall of the envelope and is connected to suitable drive mechanism 24 which may be operated to cause rotation of the drum 19 and consequently of the belt or scroll 16. Although shaft 23 extends through the envelope wall, this is achieved by a suitable vacuum seal whereby a vacuum is maintained in the envelope, or at least a portion of the drive means may be disposed within the vacuum chamber if preferred.

The framework 17 is provided with means for applying pressure upon the drums 18-19 to urge them in a direction away from one another whereby the belt 16 is maintained under tension. While such tensioning or pressure means may take any suitable form, the uprights 20-21 each are shown in FIG. 3 as embodying two axially aligned rods 20a-20b and 21a-21b respectively between the adjacent spaced ends of which are located springs 40. Sleeves 41 are positioned over the springs and adjacent ends of the rods to permit the rods limited sliding or telescopic movement under varying thermal expansion, contraction, and other stresses.

The scroll or belt supports tenebrescent or scotophor target material and in its simplest form comprises a thin metal shell of stainless steel, nickel or other selected metal which is made relatively thin and smooth, as well as flexible. The tenebrescent or scotophor material with which the metal belt is coated is a crystalline material such as potassium chloride, sodium chloride, zirconium silicate, calcium fluoride, barium titanate, or other selected material which upon electron bombardment changes its light absorbing or light altering characteristics. In the presently described device, bombarded areas of the tenebrescent material are altered with respect to their optical 2B transmittance and reflectance characteristics to become relatively darker than the unbombarded areas, as viewed under external illumination.

A brush contact 42 (FIG. 2) is sealed through the rear wall of the envelope and engages the edge of the scroll to provide means for supplying a voltage thereto.

The tenebrescent material has several features which make it particularly attractive for use in the display device being described. Its persistance is practically infinite at room temperature so that no appreciable decay in contrast takes place over a substantial period of time, and once written upon, no excitation is required for continuous display other than that of ambient illumination by visible light. Hence the visibility of the display is not degraded by ambient illumination but is enhanced by it.

From the foregoing it will be understood that the drive means 24 may be operated to move the target by rotation of drum or reel 19. Simultaneously therewith an incoming signal is applied to the electron gun 13 which produces an intensity-modulated electron beam which, through operation of conventional deflection and focus means 25 26, is made to focus upon and scan the upper end of the moving tenebrescent target 16, producing a visible image thereon corresponding to the incoming electrical signal. It will be apparent that as the target 16 moves, the written area thereon will move downwardly behind a window portion 26 of the envelope which is polished or otherwise prepared so as to render the visible image clearly visible without distortion.

The drive means may be operatively controlled so that the target 16 will move in synchronism with the rate of speed of the vehicle in which the device is mounted. Normally, however, the image will move relatively slowly downwardly through the entire field of view, and will retain its quality throughout its travel through the viewing area. Such driving means may, for example, be a standard 400-c.p.s. unit geared down by about 750:1 to operate at rpm, or other suitable arrangement.

After the image has passed through the viewing area it traverses the lower drum 19 and then moves upwardly on the rear side of the structure toward the writting electron beam. Therefore, it becomes necessary to erase previously written information. To accomplish this the scotophor or tenebrescent material is subjected to controlled heating, for example, at a temperature between approximately 300 and 350 C., which temperatures may, however, vary considerably. The higher the temperature, the faster the erasure takes place, and at 350 C. erasure is practically instantaneous. For simplicity, the heating means may be located outside the envelope as shown in FIG. 2, and comprises a line source such as a hot filament 27. Filament 27 is located at one focus of a semi-elliptical reflector 28, the other focus of which is disposed in the plane of the scroll or target surface, as indicated by dot-dash lines. In this way, when the filament 27 is energized, the reflector 28 directs heat onto the target through the rear wall of the envelope, which wall may be made especially transmissive to infrared radiation, if desired. The heat radiation impinges upon the target in a horizontal line at the point of impact, thus erasing the written visible image line by line as the target moves. In this way only a restricted area of the target becomes heated. Furthermore, the heating takes place at a point on the target which is far removed from the point nearest the writing electron gun, allowing maximum time for a target area to cool prior to subsequent writing on that area. Final cooling is enhanced by the contact of the moving scroll or target with drum 18 which lies nearest the gun 13. By focusing the infrared energy into a narrow line, the necessary erasing temperature may be achieved with a minimum of heat energy transmitted to the scroll.

The light source 29 shown in FIG. 2 is merely intended to represent any available ambient illumination for viewing the image on the target. However, green light has d. been found to be especially elficient for superior enhancement of the image when potassium chloride is used as the electron-sensitive material.

A modification of the tenebrescent target is achieved by employing a mosaic-type surface in which case the scroll may comprise a plurality of layers of electroplated metal to permit selective etching. The scroll in this case is made by electroplating suitable metals on a cylindrical form and subsequently removing the form by etching, melting or otherwise removing the form material, leaving a seamless ribbon or belt for the scroll. For example, referring to FIG. 4, the scroll has a first layer 36 of a chemically resistant material such as gold or the like which may, if desired, be strengthened by being plated onto a stronger support layer (not shown) such as nickel or other metal. On layer 30 is deposited a readily etchible layer 31 of metal such as copper, over which is coated an outer layer 32 of another etchible material such as nickel. Layer 32, however, should be etchible at a slower rate than layer 31. A chemically resistant material such as a wax, lacquer, or photoresistive material such as used in the photoengraving art is then applied onto the exposed surface of layer 32 in a mosaic pattern of deposits 33 by mechanical printing, photodeposition, or the like. This mosaic pattern preferably has a periodicity dependent upon the desired image definition, perhaps in the order of 0.002 inch. The multilayer scroll is then subjected to etching by a suitable etchant such as nitric acid, which will etch through the outer layer 32 and attach the intermediate layer 31 in such a way as to form undercut pedestals as shown in FIG. 5. Thereafter, the chemically resistant material 33 is removed and deposits 34 of the selected tenebrescent or scotophor material are evaporated onto the target surface on the tops of the pedestals and between the pedestals on layer 30, providing a discontinuous mosaic pattern, as shown in FIG. 6. The purpose of this is to provide a multiplicity of very small islands, thereby avoiding excessive smearing of the tenebrescent display which might otherwise occur due to electron scattering or the like.

In either the continuous or mosaic scroll, the display is moved as a uniform visual image through the viewing area after it is written by the scanning electron beam, and is thereafter erased after passing through the viewing area.

Certain modifications will appear to those skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the appended claims.

What is claimed is:

1. A display tube comprising a vacuurnized envelope, an electron gun in the envelope for producing a beam of electrons, a target structure in the envelope comprising an endless belt having a surface of electron-sensitive material disposed in the path of the electron beam, means for causing the electron beam to transversely scan the belt to produce an image thereon corresponding to an electrical signal applied to the electron gun, and means for rotating the belt to present nonimage-bearing material to the scanning electron beam, said target structure comprising a framework including a pair of longitudinally extending spaced side rods and a pair of rotatable shafts supported between the rods at opposite ends thereof, said rods carrying spring members thereon in resilient engagement with the walls of said envelope for maintaining the frame in spaced relation therewith and for permitting expansion and contraction under varying thermal stresses, said belt being mounted over the shafts and rotatable therewith.

2. A display tube as set forth in claim 1 wherein the framework carries tensioning means for maintaining the belt taut and firming in engagement with the shafts.

3. A display tube as set forth in claim 2 wherein said longitudinally extending spaced side rods each embodies a pair of rod-like elements disposed in spaced aligned endto-end relation with the adjacent end portions being slidably mounted within a sleeve, and said tensioning means comprises a spring located within said sleeve between the adjacent ends of said rod-like members for urging the rodlike members axially away from one another.

4. A display tube comprising a vacuumized envelope, an electron gun in the envelope for producing a beam of electrons, at target structure in the envelope comprising an endless belt having a scroll thereon of electron-sensitive material disposed in the path of the electron beam, said scroll comprising a first layer of chemically resistant material, a second layer of etchible material disposed on said first layer, and a third layer of etchible material on said second layer, said third layer being etchible at a slower rate than said second layer, portions of said second and third layers being removed in a predetermined pattern to provide spaced pedestals on said first layer, and deposits of tenebrescent material on the exposed outer surfaces of the pedestals and on the first layer between pedestals, means for causing the electron beam to transversely scan the scroll adjacent one end of the structure to produce an image thereon corresponding to an electrical signal applied to the electron gun, means for moving the belt to move the image from the scanned end of the target structure to the opposite end thereof, and means for erasing the image on the scroll at a point remote from the scanned end of the target structure.

References fiited by the Examiner UNITED STATES PATENTS Re. 22,734 3/ 1946 Rosenthal 178-7.87 2,351,889 6/1944 Strubig 1787.87 2,585,846 2/1952 Rosenthal 1787.87

DAVID G. REDINBAUGH, Primary Examiner.

J. MCI-LUGH, Assistant Examiner. 

1. A DISPLAY TUBE COMPRISING A VACUUMIZED ENVELOPE, AN ELECTRON GUN IN THE ENVELOPE FOR PRODUCING A BEAM OF ELECTRONS, A TARGET STRUCTURE IN THE ENVELOPE COMPRISING AN ENDLESS BELT HAVING A SURFACE OF ELECTRON-SENSITIVE MATERIAL DISPOSED IN THE PATH OF THE ELECTRON BEAM, MEANS FOR CAUSING THE ELECTRON BEAM TO TRANSVERSELY SCAN THE BELT TO PRODUCE AN IMAGE THEREON CORRESPONDING TO AN ELECTRICAL SIGNAL APPLIED TO THE ELECTRON GUN, AND MEANS FOR ROTATING THE BELT TO PRESENT NONIMAGE-BEARING MATERIAL TO THE SCANNING ELECTRON BEAM, SAID TARGET STRUCTURE COMPRISING A FRAMEWORK INCLUDING A PAIR OF LONGITUDINALLY EXTENDING SPACED SIDE RODS AND A PAIR OF ROTATABLE SHAFTS SUPPORTED BETWEEN THE RODS AT OPPOSITE ENDS THEREOF, SAID RODS CARRYING SPRING MEMBERS THEREON IN RESILIENT ENGAGEMENT WITH THE WALLS OF SAID ENVELOPE FOR MAINTAINING THE FRAME IN SPACED RELATION THEREWITH AND FRO PERMITTING EXPANSION AND CONTRACTION UNDER VARYING THERMAL STRESSES, SAID BELT BEING MOUNTED OVER THE SHAFTS AND ROTATABLE THEREWITH.
 4. A DISPLAY TUBE COMPRISING A VACUMMIZED ENVELOPE, AND ELECTRON GUN IN THE ENVELOPE FOR PRODUCING A BEAM OF ELECTRONS, A TARGET STRUCTURE IN THE ENVELOPE COMPRISING AN ENDLESS BELT HAVING A SCROLL THEREON OF ELECTRON-SENSITIVE MATERIAL DISPOSED IN THE PATH OF THE ELECTRON BEAM, SAID SCROLL COMPRISING A FIRST LAYER OF CHEMICALLY RESISTANT MATERIAL, A SECOND LAYER OF ETCHIBEL MATERIAL DISPOSED ON SAID FIRST LAYER, AND A THIRD LAYER OF ETCHIBEL MATERIAL ON SAID SECOND LAYER, SAID THIRD LAYER BEING ETCHIBLE AT A SLOWER RATE THAN SAID SECOND LAYER, PORTIONS OF SAID SECOND AND THIRD LAYER BEING REMOVED IN A PREDETERMINED PATTERN TO PROVIDE SPACED PEDESTALS ON SAID FIRST LAYER, AND DEPOSITS OF TENEBRESCENT MATERIAL ON THE EXPOSED OUTER SURFACES OF THE PEDESTALS AND ON THE FIRST LAYER BETWEEN PEDESTALS, MEANS FOR CAUSING THE ELECTRON BEAM TO TRANSVERSELY SCAN THE SCROLL ADJACENT ONE END OF THE STRUCTURE TO PRODUCE AN IMAGE THEREON CORRESPONDING TO AN ELECTRICAL SIGNAL APPLIED TO THE ELECTRON GUN, MEANS FOR MOVING THE BELT TO MOVE THE IMAGE FROM THE SCANNED END OF THE TARGET STRUCTURE TO THE OPPOSITE END THEREOF, AND MEANS FOR ERASING THE IMAGE ON THE SCROLL AT A POINT REMOTE FROM THE SCANNED END OF THE TARGET STRUCTURE. 